VERY BLUE UV-CONTINUUM SLOPE β OF LOW LUMINOSITY z ∼ 7 GALAXIES FROM WFC3/IR: EVIDENCE FOR EXTREMELY LOW METALLICITIES?

By R. Bouwens, G. Illingworth, P. Oesch, M. Trenti, M. Stiavelli, C. Carollo, M. Franx, P. V. van Dokkum, I. Labbé, D. Magee. 2009

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We use the ultra-deep WFC3/IR data over the Hubble Ultra Deep Field and the Early Release Science WFC3/IR data over the CDF-South GOODS field to quantify the broadband spectral properties of candidate star-forming galaxies at z ∼ 7. We determine the UV-continuum slope β in these galaxies, and compare the slopes with galaxies at later times to measure the evolution in β. For luminous L*z=3 galaxies, we measure a mean UV-continuum slope β of −2.0 ± 0.2, which is comparable to the β ∼ −2 derived at similar luminosities at z ∼ 5–6. However, for the lower luminosity 0.1L*z=3 galaxies, we measure a mean β of −3.0 ± 0.2. This is substantially bluer than is found for similar luminosity galaxies at z ∼ 4, just 800 Myr later, and even at z ∼ 5–6. In principle, the observed β of −3.0 can be matched by a very young, dust-free stellar population, but when nebular emission is included the expected β becomes ⩾−2.7. To produce these very blue βs (i.e., β ∼ −3), extremely low metallicities and mechanisms to reduce the red nebular emission seem to be required. For example, a large escape fraction (i.e., fesc ≳ 0.3) could minimize the contribution from this red nebular emission. If this is correct and the escape fraction in faint z ∼ 7 galaxies is ≳0.3, it may help to explain how galaxies reionize the universe.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering, Instrumentation

View Paper: https://www.semanticscholar.org/paper/dbce91369540b634f393e945bd3d70f3815cadc2

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Citations in the corpus

Predicted UV properties of very metal-poor starburst galaxies (2010, background): “Other groups have invoked “unusual” IMFs, extremely metal-poor stellar populations, and/or leakage of Lyman continuum radiation to explain the apparently very blue UV slopes found for some very high redshift (z ∼ 7) galaxies (Bouwens et al. 2010).”
COMPLETING THE CENSUS OF Lyα EMITTERS AT THE REIONIZATION EPOCH (2011, methodology): “Recent studies using HST/WFC3 identified more and fainter galaxies at even higher z, suggesting a faint-end slope that is sufficiently steep (Oesch et al. 2010, Bouwens et al. 2010b) to fully reionize the universe.”
THE EVOLUTION OF THE GALAXY REST-FRAME ULTRAVIOLET LUMINOSITY FUNCTION OVER THE FIRST TWO BILLION YEARS (2014, background): “…due to a decrease in dust attenuation, although the brightest/ most massive galaxies do appear to have comparable levels of dust attenuation at z = 4–7 (e.g., Stanway et al. 2005; Bouwens et al. 2010b; Finkelstein et al. 2010, 2012b; Wilkins et al. 2011; Dunlop et al. 2013; Bouwens et al. 2014).”
AN INTENSELY STAR-FORMING GALAXY AT z ∼ 7 WITH LOW DUST AND METAL CONTENT REVEALED BY DEEP ALMA AND HST OBSERVATIONS (2013, methodology): “…abundance and integrated properties of the earliest galaxies beyond a redshift of z ≃ 6 selected via optical and near-infrared (NIR) photometry (e.g. Bouwens et al. 2010a; McLure et al. 2010; Castellano et al. 2010; Ouchi et al. 2010; Ellis et al. 2013; McLure et al. 2012; Schenker et al. 2012).”
PROBING THE DAWN OF GALAXIES AT z ∼ 9–12: NEW CONSTRAINTS FROM HUDF12/XDF AND CANDELS DATA (2013, methodology): “The colors of the simulated galaxy population are chosen to follow a distribution of UV continuum slopes with β = −2.4 ± 0.4 (see e.g. Bouwens et al. 2009, 2010; Finkelstein et al. 2010; Stanway et al. 2005), and are modulated by the IGM absorption model of Madau (1995) over a range of redshifts z…”
ALMA IMAGING OF GAS AND DUST IN A GALAXY PROTOCLUSTER AT REDSHIFT 5.3: [C ii] EMISSION IN “TYPICAL” GALAXIES AND DUSTY STARBURSTS ≈1 BILLION YEARS AFTER THE BIG BANG (2014, result): “The finding of low dust extinction is consistent with recent estimates for LBGs at comparable and higher redshifts in the rest–frame optical (e.g., Bouwens et al. 2010), suggesting that detection of such galaxies in the FIR continuum may require substantial integration times even with ALMA.”
THE SPECTRAL EVOLUTION OF THE FIRST GALAXIES. I. JAMES WEBB SPACE TELESCOPE DETECTION LIMITS AND COLOR CRITERIA FOR POPULATION III GALAXIES (2011, methodology): “…is seen to become progressively steeper when going towards lower metallicities and more top-heavy IMFs – a fact previously noted by e.g. Bromm et al. (2001), Schaerer (2003), Tumlinson et al. (2003), Schaerer & Pelló (2005), Bouwens et al. (2010), Taniguchi et al. (2010) and Raiter et al. (2010b).”
UV-CONTINUUM SLOPES AT z ∼ 4–7 FROM THE HUDF09+ERS+CANDELS OBSERVATIONS: DISCOVERY OF A WELL-DEFINED UV COLOR–MAGNITUDE RELATIONSHIP FOR z ⩾ 4 STAR-FORMING GALAXIES (2011, methodology): “This blue β is also not inconsistent with what one can achieve with standard stellar population modeling (where the UV -continuum slope β can become as steep as ∼−2.7: Schaerer 2003; Bouwens et al. 2010a; Robertson et al. 2010).”
Keck spectroscopy of faint 3 < z < 7 Lyman break galaxies – I. New constraints on cosmic reionization from the luminosity and redshift-dependent fraction of Lyman α emission (2010, background): “Additionally, as UV slopes grow bluer than β = −2.0, the variation in the UV slope is possibly driven by factors other than dust obscuration (e.g. Stanway et al. 2005; Bouwens et al. 2010a).”
THE BRIGHTEST OF REIONIZING GALAXIES SURVEY: CONSTRAINTS ON THE BRIGHT END OF THE z ∼ 8 LUMINOSITY FUNCTION (2012, unknown): “…Bouwens et al. (2011b) −3.23+0.74−0.27 −20.10 ± 0.52 −1.91 ± 0.32 Lorenzoni et al. (2011) −3.0 −19.5 −1.7 (fixed) Trenti et al. (2011) −3.4 (fixed) −20.2 ± 0.3 −2.0 (fixed) McLure et al. (2010) −3.46 −20.04 (fixed) −1.71 (fixed) Bouwens et al. (2010) −2.96 (fixed) −19.5 ± 0.3 −1.74 (fixed) Note.”
KECK SPECTROSCOPY OF FAINT 3 < z < 8 LYMAN BREAK GALAXIES: EVIDENCE FOR A DECLINING FRACTION OF EMISSION LINE SOURCES IN THE REDSHIFT RANGE 6 < z < 8 (2011, methodology): “…galaxies beyond z ≃ 7 through multi-color imaging undertaken with the infrared Wide Field Camera (WFC3/IR) onboard Hubble Space Telescope (HST) (e.g., Bouwens et al. 2010b; Bunker et al. 1 Department of Astrophysics, California Institute of Technology, MS 105-24, Pasadena, CA 91125 2 Kavli…”
THE 2012 HUBBLE ULTRA DEEP FIELD (UDF12): OBSERVATIONAL OVERVIEW (2012, background): “…variety of results have been obtained on the ultraviolet spectral slopes and stellar populations of these early star-forming galaxies at z∼ 7− 8 (Bouwens et al. 2009, 2010, 2012, Ono et al. 2010, Bunker et al. 2010, Finkelstein et al. 2010, 2012b,a, Yan et al. 2011b,a, McLure et al. 2010,…”
SPECTROSCOPIC CONFIRMATION OF THREE z-DROPOUT GALAXIES AT z = 6.844–7.213: DEMOGRAPHICS OF Lyα EMISSION IN z ∼ 7 GALAXIES (2011, methodology): “…redshift (e.g., Ouchi et al. 2009; McLure et al. 2010; Castellano et al. 2010a; Bouwens et al. 2010a; Wilkins et al. 2010), bluer UV continua (e.g., Bouwens et al. 2010b)13, and relatively smaller stellar masses compared to lower redshift galaxies selected by similar techniques (e.g., Labbé et…”
STAR FORMATION RATES AND STELLAR MASSES OF z = 7–8 GALAXIES FROM IRAC OBSERVATIONS OF THE WFC3/IR EARLY RELEASE SCIENCE AND THE HUDF FIELDS (2009, methodology): “=3) to β ∼ −3.0 (0.1 L ∗ z=3), as re- ported by Bouwens et al. (2010b).”
THE HETDEX PILOT SURVEY. II. THE EVOLUTION OF THE Lyα ESCAPE FRACTION FROM THE ULTRAVIOLET SLOPE AND LUMINOSITY FUNCTION OF 1.9 (2010, methodology): “…history of the universe from Bouwens et al. (2010b), which has been derived from the best to date collection of dust extinction corrected UV luminosity functions at a series of redshifts between 0 and 8, and shows a typical uncertainty of 0.17 dex (Bouwens et al. 2010b, and reference therein).”
CONNECTING THE GAMMA RAY BURST RATE AND THE COSMIC STAR FORMATION HISTORY: IMPLICATIONS FOR REIONIZATION AND GALAXY EVOLUTION (2011, methodology): “…explanation given we would require all UV-selected star forming galaxies to be heavily extincted and most studies have utilized their UV continuum slopes to infer the absence of any significant reddening (Bouwens et al. 2010c; Finkelstein et al. 2010; McLure et al. 2011; Dunlop et al. 2011).”